1. Field of the Invention
The present invention relates to a pipe for use in pipe jacking.
2.Prior Art
Hitherto, as illustrated in FIG. 2, a pipe 50 for pipe jacking has been used in which, for the purpose of protection of an external surface, a ductile cast iron pipe body 51 of socket and spigot type is coated with reinforced concrete or mortar 52 to form a uniform common external surface. When carrying out the pipe jacking, a flange 53 provided on the spigot side at the front end of a succeeding pipe is brought into contact with an end face of the socket at the rear end of a preceding pipe, thereby transmitting a required jacking force. Reference numeral 54 indicates a mortar lining provided on the internal surface of the pipe body 51, numeral 55 indicates an annular water-sealing rubber packing, numeral 56 indicates bolt and nut pair, the blot being screwed in a tapped hole provided at the end face of the spigot of the preceding pipe to connect the socket at the end face of the preceding pipe to the flange 53 of the succeeding pipe, then fastened with the nut. Reference numeral 57 indicates a reinforcing rib, and numeral 58 indicates a welded reinforcing bar or a wire net.
In the pipe 50 of the above construction according to the prior art, the pipe body 51 is coated with reinforced concrete or mortar 52 to form a uniform common external surface. If the external surface of the coating mortar 52 is rough, frictional resistance during jacking increases, and therefore it is necessary for the rough external surface of the mortar 52 to be manually finished before jacking to make the rough external surface smooth. Further, it may be said that frictional resistance between the coating mortar 52 and the earth is generally so large that smooth jacking is difficult. As a result, relatively large-scale equipment is needed, and if carrying jacking is carried forcibly, the coating mortar 52 itself is easily broken or damaged. Moreover, when it becomes necessary to install some branch pipe, valve or the like midway of a pipe line of pipes after installing the pipe line by pipe jacking, a pipe forming the pipe line must be cut at the working spot. A serious problem exists in that a pipe such as the aforementioned pipe 50 incorporating the reinforcing bars or wire net 58 in the coating mortar 52 is very tough and difficult to cut, eventually resulting in troublesome work or delay in the work.